Indicating plug fuse



July 23, 1935. F. c. LA MAR INDICATING PLUG FUSE Filed Jan. 11, 1934INVENTOR i ATTORNEY equal to that of a plug fuse in those situations.

Patented July 23, 1935 UNITED STATES PATENT OFFICE mmcarmo PLUG'FUSEFrank 0. La Mar, New York, is. r. Application January 11,1934, SerialNo. 706,171 6 Claims. (Cl. 200-121) well known form of thermal fuse isthat known as a "plug fuse", Ordinary plug fuses consist, generally, ofan insulating body having twoterminals on the outside thereof, soconstructed and arranged as to be readily broughtin contact with theterminals of an electrical circuit, by way of what is known usually asafuse block. These fuses are \miversally used: are made by manydifferent. manufacturers; and must all be usable in practically any ofthe well known forms of fuse blocks; so that they have become, in truth,standard, and may well be referred to as, standard fuse plugs. At anyrate they are substantially standard as regards their general externaldimensions.

Various forms of plug fuses have been made, especiallyfor the purpose ofenabling one to quickly discern whether or not the fusible or thermalelement 'is intact. It is quite the universal impression that successhas not been fully attained in regard to the feature of indicating theintegrity of the fusible element.

A principal object of applicant's invention is to provide a device,which may well be called a combined fuse and fuse integrity indicatingdevice. In providing'such a device, applicant has had in mind that itpreferably should be in external dimensions substantially'the size ofthe standard plug fuse, so that it may be used with a facility where aplug fuse is now used.

A further object which applicant has in mind in producing his combinedfuse and fuse integrity indicator is that the cost must be reduced to apoint where, if possible, it approximates the present cost of ordinaryplug fuses. To this end, applicant has, as a further object of hisinvention, the production of a device in two parts, separable one' fromthe other, one part supporting and protecting the thermal element, whichpart is removable, and the other part performing the indicatingfunctions desired by applicant,

"and combinable with the first part to make a complete indicating fusepart.

A further object of applicant's invention is to produce a combined fuseand fuse integrity indicator which will have substantially the same ex-5 ternal dimensions as a standard plug fuse.

Other objects and advantages will appear as the description of theparticular physical embodiments selected to illustrate the inventionprogresses, and the novel features will be par- 16 ticularly pointed outin the appended claims.

In describing the invention in detail and the particular physicalembodiments selected to illus- 4 trate the invention, reference will behad to the accompanying drawing and the several views 15 thereon, inwhich like characters of reference designate like parts throughout theseveral views, and in which:

Figure 1 is a cross-sectional view of a plug fuse embodying applicant'sinvention; Fig. 2 is a 20 top plan view of the device as shown by Fig.i; Fig. 3 is a cross-sectional view of the device as shown by Fig. 1 onthe plane indicated by the line III-III viewed in the direction of thearrows at the ends of the line; Fig. 4 is a cross-sectional view of thedevice as shown by Fig. l on the plane indicated by the line IV--IV ofFig. I, viewed in the direction of the arrows at the ends of the line;Fig. 5 is an elevational view of the indicator portion of applicant'scombined fuse and fuse integrity indicator, with some parts broken awayto more clearly show the construction.

Figure 1, broadly considered, shows a combined plug fuse and fuseintegrity indicator having as essential parts the usual end contactterminal I; the screw threaded shell terminal 2; and a thermal fusibleelement 3 connecting terminal I and screw thread shell 2. These partsare comparable with and constitute the principal parts of the usual andordinary fusible plug. In addition to the plug portion there is anindicator portion which broadly includes a gaseous discharge lamp 4,preferablyof the neon filled type, having one terminal 5 connected tothe contact terminal I and the other terminal connected, through a highohmic resistance 6, to an electrical conducting rod 1 electricallyconnecting to screw shell 2. A construction such as has been describedserves all of the functions of the ordinary plug fuse and in additionoperates to indicate the integrity of the fusible element 3 because whenthat element is intact the lamp 4 is not illuminated, but when thethermal element 3 is destroyed then the lamp 4 is illuminated indicatingthe destruction of the fusible element 3.

andl2' which cooperate with the disc 8 to retain it in place.

In order to separate the lamp 4 from the interior of the fuse plugwithin which the fusible element 3 is positioned, applicant provides aninterior cylindrical tube 13 which has an internal diametercorresponding with the diameter of the upper opening H of the body8 andhas anexternal diameter such that it just fits within the bore l5 whichis slightly larger than-the opening H of the body 8.. p I

Applicant provides a closure for IS thereover which fits {tightlyagainst the wall of the cylindrical tube ,andis preferably provided witha depending'bulge I! for a purpose .to be" hereinafter'described,

Applicant provides an indicating carrier" designated as awhole by C.This carrieris pref erablyformed in two parts 18 'arid'lS divideddesignated 22. The arms 2| and 22 rest one within the other so that. thetop surface of 2l,is one continuous unbrokenline. and the bottom surfaceof the two is one continuous unbroken line. J

members together, applicant prefers to use a me-.

tallic-band- 23 at the upper portion, which although, perhaps notabsolutely necessary, is desirable, and a metallic cap 24 at the lowerportion.

This metallic cap 24 fits tightly around the interfitted hollowsemi-cylindrical members and is provided with anorifice 25 for'thepassage therethrough of one lead 5 of the lamp 4.

Thelead 26 of the lamp 4 is preferablycarried up and alongside of thelamp 4 and then connected to one terminal of the resistance 8. Thisresistance 6 is of the grid leak type and where appllcants device is tobe used on 110 volt circuits is of the order of about 50,000 ohmsresistance. The other terminal of the resistance} is connected by theconductor 21 to the metallicrod 1.

Metallic rod 1 is positioned, preferably, by

. moulding in the arm 22 ofthe hollow semi-cylinder member is and ispositioned to pass down through a bore 215 formed in the body 8 so thatits lower preferably scarfed or'pointed end 28 may contact with themetallic screw threaded shell 2. The assembly of the device isaccomplished by first soldering one end of the fusible member 3 in theterminal I and at the same time soldering the bulge H of the metalliccap Hi of the cylindrical tube l3 to the same terminal. The disc 9carrying with it the associated parts is then put in place, as shown byFig. v1, with one end of the fusible link 3 passing through an orifice28 and positioned to contact withscrew threaded shell..

2, and the upper end of the cylindrical tube I3 I the lower end. .of thecylinder tube 13 by placing a metallic cap ti'on. along the, planeindicatedi byfl ine 2i) and each being for. a. greater portion of itslength'substan tially the half of a hollow cylinder so thatvappli-j cantcalls the. members hollow l,.s'eml-.cylindrical.' Each of themernbers-ld and lllhas outstanding arms at its upper. portion thatattached to [8'1 being designated 2| and that attached tojdbeing seatingin the bore I5, whereupon the screw thread shell 2 is screwed onto thebody 0 and holds all parts in proper position.

In order to assemble the indicator carrier C the lamp 4 has one terminalthereof, 5, passed through the orifice 25 in the cap 24 and a drop ofsolder applied, then the other terminal is connected to a resistance 6which in turn is connected to rod 1, after which the two portions of thecarrier are placed together as shown in Fig. 1 with the band 23 slippedup over them and the cap 24 placed over; their lower'ends, theresistance 6 resting in "a cavity formed therefor.

The carrier C is positioned by inserting it in the orifice it while therod 1 is inserted in the bore 21' after which it is forced home, asshown by Fig. 1, with the small drop of solder 30 resting in the bulgell of the metallic cap it and the rod plug formed exactly asis the bodytwith its associat'edpar'ts Although I have particularly'descrlbed'oneparticularjphysicalembod'iment ofj'rny lnventiouand explained theoperation, construction and princi- 'ple thereof,nevertheless, I desireto have'itunderstood that the form ,selectedismerely illustrative,

but does notexhaust the possible P ysical embodimer ts of theideaofmeans underlying jmy invenn attain new a nd a'essas m tersBatentfoftheUnited States, is; j ln a s'eiha ine in omb n on an Outer"cylindrical screwjthreaded metallicshell fcbntact; a metallic contactpositioned axially 'of the shell;

a1 t mal elemen rmet 'e h 'tbnta'cts: a lam a s't 'o te'rm na sim w portin and rnt sm inemgrfand. s ns we a w h fitsilongitddirfifl axisaxially pfthe metallic shell, fsaidmean's removable ,bodily'andincluding means I A for]forming eleetrical connections to the con- .Inorder to hold the hollow semi-cylindrical .tac't's, said last fmentionedmeans including a rod carried by the lampsupporting means position tomake contactwith'the screw threaded "metalli shell. I

metallic contact closing one end'of the hollow body; a cylindrical'tubewithin the hollow body, .one end of thetube fitting within a bore of thehollow body of greater diameter than the 'end opening of the hollowbody, the other end of the cylindrical tube being provided with ametallic cap embracing a portion of the outer surface of the cylindricaltube and being soldered together with one end of a. fusible element tothe centraliy disposed contact of the disc, the other end of the fusibleelement being carried through an orifice in the body and positionedagainst the outside periphery of the-body; and a screw threaded shelladapted to cooperate with the screw threads of the body and providedwith means for holding the discin place.- i a 3. As a plug portion of acombined fusible plug and indicator,. thecombination of a hollowsubstantially cylindrical body provided with an internal wall supportingand defining, from the remainder of thespace within the hollow body, aspace'communicating with one openend of thehollow body; a fusible linkpositioned within the said remaining space; means for closing the otheropen 75 end of the cylindrical body, a substantially central metallicterminal carried by the said means for closing; a metallic shellsurrounding a portion of the outside of the hollow body; and a fusiblelink connecting the shell and the metallic terminal.

4. As an indicator lamp carrier of a combined fuse and fuse integrityindicator, in combination: two substantially semi-cylindrical members;means for holding said members together to substantially form a tubeclosed at one end; each of said members bearing an arm interfitting withan arm of the other member; a metallic rod attached to one of said armsand depending therefrom so positioned that when the combinedsemicylindrical portions are positioned centrally of a plug fuse thedepending arm will be positioned to pass through a bore of the plugfuseand contact the ordinary screw shell on the outer periphery thereof; andan indicator lamp having a resistance in series therewith connectedbetween the said rod and the metallic holding means closing one end ofthe assembled semi-cylindrical mem-- bers.

5. An indicating plug fuse of substantially standard contour andover-all dimensions, having in combination; a hollow body of insulatingmaterial; an outer cylindrical threaded metallic shell contact; anexterior metallic contact positioned axially of the body, and having acontact portion extending within said body; a thermal element connectingthe contacts; a fuse integrity indicating lamp including an evacuatedshell having two terminals; and means supporting and enclosing the lampand provided with contacts for engagement with portions of said plugcontacts when said lamp and its supporting means are assembled with saidplug; said lamp contacts including means positioned to make contact withthe interior of the screw threaded metallic contact.

6. An indicating plug fuse of substantially standard contour andover-all dimensions, having in combination; a hollow body of insulatingmaterial; an outer cylindrical threaded metallic shell contact; anexterior metallic contact positioned axially of the body, and having acontact portion extending within said body; a thermal element connectingthe contacts; and having its most readily fusible portion confinedwithin said hollow body; a. fuse-integrity-indicating lamp having twoterminals; and means supporting and enclosing the lamp and provided withcontacts for engagement with portions of said plug contacts when saidlamp and its supporting means are assembled with said plug; said lampcontacts including a rod positioned to make contact with the interior ofthe screw threaded metallic contact, said lamp-support, lamp and lampcontacts being removable bodily from said plug, by a right line movementof said lamp support.

FRANK C. LA MAR.

